The objective of the project is to determine the effects of physical stresses on platelets. Preliminary studies have shown the relatively low (50 dynes/cm2) shear stresses stimulate the release reaction and subsequent aggregation, and have raised the possibility that thrombus formation could result from the effects of this physical force on circulating plateleets. Work is being carried out to establish the effects of exposure time to knwon, uniform shear fields, the complication of cell-cell interaction - including studies in whole blood, the related cell-solid surface interactions, and the influence of platelet anti-aggregating agents. The results obtained to date and analysis of results of other workers have important implications in understanding of the mechanics of thromboembolism and thrombocytopenia. The work in the coming year will be concentrated in two areas; (1) studies in whole blood (as opposed to platelet-rich plasma) and (2) the effects of antipltelet agents.